Electbic



o. A. COLBY ELECTRIC FURNACE. APPLICATION man cTi is, 1917.

Patented June 10, 1919.

wnNEssEs z mvENToR 0m, A. (0M/V ATTORNEY vconducting lmaterial,

UNITED. sra'rns PATENT orricn.

Voli/A n. copiar, or LARIMER, PENNSYLVANIA, AssIGnon 'ro WEsrINGHoUsE ELECTRIC ANDMANUFACTURING COMPANY, A oonromrrron or PENNSYLVANIA.

:ELECTRIC FURNACE Applceti'm filed October 13, 191'?.

To all whom it may concern:

This invention relates to electric furnaces4 and particularly to an electric-resistance furnace that may be operated continuously for comparatively long periods and be adapted to produce high temperatures for heatingmetals and also for other heating applications.

The object of the invention is to provide an electric furnace that shall have a low rate deterioration under service conditions at high temperature of 1000o C., or above, since,

4to be commercially successful, such furnaces should require only infrequent and inexpensive repairs and. renewals.

The above and other objects and the novel features of the invention will be apparent from the following description taken in connection .with the accompanying drawing that forms .a part of this application and of which Figure 1 is a sectional view of an electric furnace embodying this invention, taken transversely, of the heatin chamber or hearth, and Fig. 2 is a sectional view of the same furnace taken on the line ll of Fig. 1.

The supporting structure of the furnace comprises an exterior metal casing or frame 10 which incloses lire-brick walls 11, and a floor 12 of suitable highly refractory material that is able to withstand the highest temperature at Which the furnace is operated. The4 hearth or heating chamber 13, adapted to contain the articles or metal to be treated, has a roof arch 14 of very highly refractory material that is supported bythe interior fire-brick Walls 15.

The floor of the hearth is composed of a layer 16 of non-fusible, .low-resistance such as granulated graphite, upon a layer 17 of nonfusible high-resistance conducting material, such as granulated charcoal. The layers 1G `and. 17 are disposed directly beneath the furnace chamber 13 and together constitute the resister of thel furnace. A lining 18, of refractory material, such as a composition or" carborundum sand and silicate of soda, or

Specification of Letters Patent.

Patented June 1o, 1919.

serial. no. 19e/n2.

carborunduin sand, graphite and Crucible clay, extends beneath and along the sides of the resistor bed and forms a heat-inf sulating highly refractory container for the resistor that insulates the latter from rthe lire-,brick jloc..." 12 of the furnace. On opposite sides of the furnace chamber 13, and between the walls 11 and 15, are hoppers 19 that. are provided with inlets at their upper ends. Terminal electrodes :20, of solid graphite or amorphous carbon, extend up- `wardly into the hoppers 19 and have their upper tapering ends disposedopposite the ends ofr the resistor bed, consisting of the layers 1G and 17. The electrodes 20 have heavy iron lugs 21 secured thereto that project outside the hoppers and furnace, and to which the current supply mains are connected.

The graphite electrodes 20 are expensive and, if exposed to the air, would be rapidly consumed at the high temperature at which the furnace is operated. In order to'prevent the consumption of these electrodes, the spaces between themand the ends of the resistor bed are filled with an electrical conducting, thermal-insulating oxidizable material which is packed in the hoppers to seal and protect the electrodes from theatmosphere. Furthermore, the cross-sectionlof the material, in the spaces between the electrodes and the resistor, is considerably'greater than that of the resistor bed to reduce the conduction of heat from the .resistor to the electrodes. 1 have found that the material best suited for packing into the spaces between the resistor and the electrode is granulated graphite, which is 'non-fusible, of low electrical resistance and of the same composition as the material comprising the floor of the heating chamber. lThe granulated graphite in the hoppers and the material in the resistor bed are gradually consumed by oxidation and may be replaced by' charging more material into the hoppers 19 and 100' Y and-i1 from 30 granular material was consumed at the rate of about two pounds per day, and, by filling the hoppers to the no attention, other ing,for a period of several weeks. This furnace required about 90 volts for starting ,to L10 volts to maintain it at atemperature of about 950o C, and, in continuous heating of steel for forging purtop, the furnace required poses, -the furnace could be, worked up to around 4,0 Kw.

lVitli a resistor bed composed entirely of graphite and surrounded at the bottom and sides by insulation, such Vas the insulation 18, I discoveredthat, due to the fact that carbon has a negative temperature coefficient, the current through the resistor bedconcentrated in the zone of highest temperature, which iswithin the bed about at the.

joint between the layers 16and 17, since the surface of the bed constitutes the floor of the heating chamber and is, therefore, cooler l than the lower portions of the bed. Therefore,- instead of forming the. resistor bed of a material which has' substantially the same thermal-insulating and electrical-conducting properties throughout, the lower portion ofthe bed is composed of a material, Lsuch as granular charcoal, which has a lower electrical and thermal conductivity than the layer of material aboveit. When the furnace is operating, the layer 16 will generate heat faster than the layer 17, on account of the lower resistance of the former. The resistor or bed will, therefore, heat more uniformly throughout when' current flows through it, and the temperature in the bottom of the resistor mass may be kept from exceeding the limits of'the refractory lining 18 when the temperature of the floor of the heating chamber reaches about 1000o C.

The type of electrical furnace above described is suitable for heating steel to forging temperatures and for other metal-heatving operations, such as heat-treating steel brass and other metals and firing ceramics since the furnace may and enameled ware,

for comparativelv `be operated Y continuously long intervals of time.

lVhile I have shown and described the furnace construction in detail, it is to be understood that the invention is not'limited to the forni of furnace illustrated but that changes may be made therein without departing from the spirit and scope of the invention.

I claim my invention z I 1. An electric furnace comprising a heating chamber, a resistor adjacent the heating than an occasional tamp-A chamber, terminal electrodes, and a mass of thermal-insulating, electrical-conducting. material interposed between each of saidv electrodes and thev resistor to conduct current and adapted to prevent overheating and consumption of said electrodes.

2. An electric furnace comprising a heating chamber, a resistor adjacent said chamber, terminal electrodes, and a `mass of thermal-insulating, electrical-conducting material interposed between each of said electrodes and the resistor to conduct current to the latter, said mass being granular and of greater cross-section than said resistorto p'revent overheating and consumption of said electrodes. A

3. An electric furnace comprising a heating chamber, a resistor constituting the ioor of' the heating chamber, terminal electrodes located opposite the ends of the resistor, a mass of thermal-insulating, electrical conducting oxidizable granular material interposed between each electrode and the resistor to conduct current to the latter and arranged to prevent overheating and oxidation of the electrodes, and means whereby material may be added to the mass adjacent each electrode to replace the material consumed 'by oxidation.

4. In an electric furnace, the combination of a heating chamber, a resistor bed underlying said chamber comprising material having a comparatively low electrical resistance and a low thermal conductivity, terminal electrodes opposite the ends of the resistor bed, and a mass of thermal-insulating, electrical-conducting material interposed between the ends of said resistor bed and each of said electrodes, the cross-section of said mass of material being greater than the cross-section ofthe resistor bed to prevent overheating said electrodes.

In an electric furnace, the combination of a` heating chamber, a resistor bed constitutiiig the floor of said chamber and comprising thermal-insulating, electrical-conducting granular material, solid carbonaceous terminal electrodes opposite the ends of the resistor bed, a mass of granular material interposed between the ends of said resistor bed and each of said electrodes. said mass of material being of the same composition as that comprising the resistor bed and being of suiiicient cross-section toprevent overheating of the electrodes, and means whereby material may be added to said mass and bed to replace that which is consumed.

6. In an electric furnace, the combination with a heating` chamber, of a resistor constituting the floor of said chamber, hoppers located adjacent the ends of the resistor, terminal electrodes in said hoppers, and a niass of thermal-insulating, electrical-conducting granular material in each of said hoppers and filling the spaces between the ends o? saif i'=esietei^ and said, eeeiodea eea-. hoppeis ila-Ying iiiets, whereby gitanaai' mateia may be @ha 5ft into the Same iepac the portion oi i ma that is Consumed,

il? lc furnace, t? e combination W neat-mg chamber, of a; reeistoi, hopi3 teiizaiiial eeetiodee' extending upinto saic't iop'pei's 'aged' terminating pea agie ends o t eat( resistor, ami

l j; l iai* material iii each of the ioppere vthe Spaces between the of said, re r and. said ee-etiedes, eai aepa'eie iavng iiiiets above lSaid epacee,

into' tige e io to ifepiaee the poittion fo *eee iiiatei'ia L ,e is eoneiimea.

e. n an eeetrio iirnaeej the eemiiiation.

. with a heat-ing chamber, of a esistoi? Contotingthe Hooi* sai@ ehambe, kappers located adjm to the ende o the ieeieiei',

iig iiws'aiz into fsaid, ioppeis and terixiiiiatiiig opposite the emite A Asiesistei?g au@ a, mese et' theimatiiig., eleoti'icel-conducting granata? .iiiateriai in each of the hoppeis iiiiig' the spaeee-betweeii the eiide of eaici iesstoi and i 'o ends of Said eieotiodes, said hofi lng inlets above. said epaeee, whe-re- ;e to replace the potien of the maconsumed.

ctie ifi the eoiJoiiiat-ion with heating chamber, oir' resistor bed t'iermai-iiieiating, electrifiedconducting oiici-zable Oiaziuai mami-iai oonstitiiting ehe Hoor oeaid handje? hop-pere at the enne" o" said i'esietoi bed, each having a cross-section gieatei' than that of the re sister; bed, Solid earbonaoeous termina eieetiodee extending upwardlyiiito said ooppers and having tapering ends terminating opposite the ends of e'aidi'esistoi' be, teimiiial lugs secured to the owei ends of said.

v electiodee, and a. mass of therma-iiieuiating,

electrical? Conducting oxidizabie graiiuai material in each of the hoppeis iliiig the spaces between the tapering ends of sa eeotrodes and the ende of resistor oee7 Suini hopp-ers having iiiiets above Said. spaces, whereby granular iuatera may be charged i pei's Located adjacent the ,eiis 10i the re 'graiiuiai mate iat .iay be charged into 3 ooiieomee. Aheee, a resieior oim A l1. A11 eieetrie furnace comprising a heatiiig chamber, and a resistoi: adjacent sai heating diamine?, the portion of said re- Sietoi nearest Said chamber having a higher he laye? aeiow f e. in au eieetiie furnace, a heating chamoefr having a 'fio-oi: consisting of a ayei ef gyanuai ea'fboiiaeeous material, a Seeend a'vei' below said @oor ieg/ex' consisting o ii t f i of lower eleeti'ieai contetivty ti ff'oi iayeif and a iining oit highly ie iateiiai iiieosing said second ia ers together constituting the i-- 'iiinaee tion ,ating eiiainbei of a iesistoi adgaceiit Said, chamber eompzm i et iioii-i'fusiiie mateiai o3? difieren ele eondiietivity, Containei' of ca'rboruiimi-w Sami c'oiiipoeition iii Whieh said iayeie are ffiispoee", terminal eiectiodes dispoee, en rles of the ieeistoi, and masses of tiieiieiiai-iiisuiating, eiect M conducting maeialbetween sai eeetieoes all the. ieeietoi'.

iiiy testimony whereof, I have here Subscribed mi; name this 2nd ay o; iai.

he. to epiaee the potien of the the ioei' ci: Vheating chamber and Com- 

